Recently, the Radio Broadcast Data System (RBDS) has been introduced in the United States. RBDS is a means by which radio broadcasters can transmit digital data along with their broadcast signal to "smart" receivers capable of performing a variety of automatic functions. Briefly, the RBDS signal is located on a subcarrier frequency of 57 kHz. The data rate is 1187 bits per second and the subcarrier injection level is low (i.e., approximately 3 percent). In this way, no harmful interference appears in the programming carried by the broadcast.
The RBDS digital data format is organized as a plurality of categories of codes which may be used by RBDS receivers to trigger specific functions. A few of the categories of codes are as follows:
Clock Time and Date Code is time and date information continuously available in the RBDS signal for updating the time display in the receiver's clock; PA1 Program Identification Code is information relating to the radio broadcaster's station; PA1 Traffic Program Code identifies the radio broadcaster as one providing traffic information; PA1 Traffic or Emergency Announcement Code is used to interrupt current programming with a particular traffic or emergency announcement; PA1 Program Type Code is used to identify a particular station's current format (e.g., news, talk, rock, etc.); and PA1 Radio Text Code is used to transmit text data along with programming carried by the broadcast signal.
In light of this new broadcast capability, there exists an immediate need for RBDS receivers that can scan, identify and select a radio program using listener specified radio broadcast RBDS codes.